Cytoplasmic BRMS1 expression in malignant melanoma is associated with increased disease-free survival

Viví Ann Flørenes ,Anne Katrine Ree Rosnes,Ruth Holm,Danny R. Welch ,Elisabeth Emilsen,Ana Slipicevic,Gunhild M. Mælandsmo

doi:10.1186/preaccept-1890414292623626

Abstract

Breast cancer metastasis suppressor 1 (BRMS1) blocks metastasis in melanoma xenografts; however, its usefulness as a biomarker in human melanomas has not been widely studied. The goal was to measure BRMS1 expression in benign nevi, primary and metastatic melanomas and evaluate its impact on disease progression and prognosis. Paraffin-embedded tissue from 155 primary melanomas, 69 metastases and 15 nevi was examined for BRMS1 expression using immunohistochemistry. siRNA mediated BRMS1 down-regulation was used to study impact on invasion and migration in melanoma cell lines. A significantly higher percentage of nevi (87%), compared to primary melanomas (20%) and metastases (48%), expressed BRMS1 in the nucelus (p < 0.0001). Strong nuclear staining intensity was observed in 67% of nevi, and in 9% and 24% of the primary and metastatic melanomas, respectively (p < 0.0001). Comparable cytoplasmic expression was observed (nevi; 87%, primaries; 86%, metastases; 72%). However, a decline in cytoplasmic staining intensity was observed in metastases compared to nevi and primary tumors (26%, 47%, and 58%, respectively, p < 0.0001). Score index (percentage immunopositive celles multiplied with staining intensity) revealed that high cytoplasmic score index (≥ 4) was associated with thinner tumors (p = 0.04), lack of ulceration (p = 0.02) and increased disease-free survival (p = 0.036). When intensity and percentage BRMS1 positive cells were analyzed separately, intensity remained associated with tumor thickness (p = 0.024) and ulceration (p = 0.004) but was inversely associated with expression of proliferation markers (cyclin D3 (p = 0.008), cyclin A (p = 0.007), and p21Waf1/Cip1 (p = 0.009)). Cytoplasmic score index was inversely associated with nuclear p-Akt (p = 0.013) and positively associated with cytoplasmic p-ERK1/2 expression (p = 0.033). Nuclear BRMS1 expression in ≥ 10% of primary melanoma cells was associated with thicker tumors (p = 0.016) and decreased relapse-free period (p = 0.043). Nuclear BRMS1 was associated with expression of fatty acid binding protein 7 (FABP7; p = 0.011), a marker of invasion in melanomas. In line with this, repression of BRMS1 expression reduced the ability of melanoma cells to migrate and invade in vitro. Our data suggest that BRMS1 is localized in cytoplasm and nucleus of melanocytic cells and that cellular localization determines its in vivo effect. We hypothesize that cytoplasmic BRMS1 restricts melanoma progression while nuclear BRMS1 possibly promotes melanoma cell invasion. Please see related article: http://www.biomedcentral.com/1741-7015/10/19

Highlights

Melanomas accounts for only 4% of all dermatological cancers, they are responsible for approximately 80% of skin cancer-related deaths
Protein expression of Breast cancer metastasis suppressor 1 (BRMS1) was analyzed by immunohistochemistry in a panel of paraffin-embedded benign nevi and primary and metastatic melanoma tissues as well as in two melanoma cell lines
A significantly higher percentage of benign nevi (87%) as compared to primary (20%) and metastatic melanoma (48%), expressed BRMS1 in the nucleus (p < 0.0001)

Summary

Introduction

Melanomas accounts for only 4% of all dermatological cancers, they are responsible for approximately 80% of skin cancer-related deaths. Melanomas can be treated surgically and 5-year survival rate exceed 80%. Less than 15% of patients having metastatic disease (stage IV) can expect to survive 5 years as there are few or no therapeutic options. The molecular mechanisms responsible for melanoma development and progression are not completely understood. Breast cancer metastasis suppressor 1 (BRMS1) was originally identified following differential expression comparisons of chromosome 11 microcell hybrids in a human breast carcinoma cell line and was further mapped to chromosome fragment 11q13, a region frequently altered in melanomas [2]. Re-expression of BRMS1 in human breast, non-small cell lung (NSCL) and ovarian carcinomas and in melanoma cell lines resulted in marked reduction of metastasis without blocking orthotopic tumor growth [3]

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